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OB First Trimester Ultrasound Protocol
Reviewed By: Spencer Lake, MD Last Reviewed: November 2020 Contact: (866) 761-4200, Option 1 Special Note: 1st Trimester OB US in the ED & B-hCG orders
Please attempt to confirm positive beta-hCG (at least urine) before doing a 1st trimester US. When a 1st trimester US order is received from the ED, ensure a beta-hCG has been ordered. If there is time pressure from the ED/schedule to complete the examination prior to a positive result, it can be done with a pending beta-hCG CINE clips should be labeled:
-MIDLINE structures: “right to left” when longitudinal and “superior to inferior” or “fundus to cervix” when
transverse
-RIGHT/LEFT structures: “lateral to medial” when longitudinal and “superior to inferior” when transverse
**each should be 1 sweep, NOT back and forth**
Some terms used:
MSD = mean sac diameter FP = fetal pole CRL = crown-rump length FHR = fetal heart rate IUP = gestational sac + yolk sac (+/- embryo)
IMPORTANT NOTE regarding 1st trimester US: AVOID Doppler (color, spectral, power) when possible
WHY limitations on Doppler in the 1st trimester?
-There is a potential risk of harm to a developing embryo from the increased heat associated with
Doppler ultrasound (especially spectral and power)
WHEN to use Doppler (this is detailed further below), very brief summary:
REQUIRED:
OVARIES/ADNEXA:
ED patient, all: color; spectral only certain indication/appearance (i.e., torsion)
Outpatient rule out torsion: color + spectral (document both venous and arterial flow)
Abnormal ovaries/adnexa - any adnexal mass or ovarian mass not clearly corpus luteum: color; spectral only for certain
indication/appearance
ENDOMETRIUM:
ONLY if abnormal endometrial findings without IUP or potential for IUP (i.e., gestational trophoblastic disease, retained
products of conception): color; if present, add spectral
OPTIONAL:
Suspected fetal demise (no HR) + CRL > = 7mm
TECHNIQUE: TA & TV vs. TA or TV only
ED patient: TA + TV for all* unless contraindicated or patient declines
*Note: proceeding to transvaginal imaging will be necessary in the majority of cases for optimal visualization and accurate measurements. If the sonographer believes that the transabdominal images are optimal and that transvaginal imaging is not needed, clearance must be given by the radiologist prior to release of the patient.
OUTPATIENT based on CRL dating: 1. CRL < = 8.6 weeks: TA+ TV* or TV only (if so ordered)
*Note: proceeding to transvaginal imaging will be necessary in the majority of cases for optimal visualization and accurate measurements. If the sonographer believes that the transabdominal images are optimal and that transvaginal imaging is not needed, clearance must be given by the radiologist prior to release of the patient.
2. CRL 9 – 11 weeks: Start with TA
Add TV: 1. If there is a >= 5 day discrepancy between LMP and CRL 2. If patient or physician is uncertain of LMP
**TA only will be OK if good views and < 5 day discrepancy between LMP and CRL**
3. CRL = > 11.1 weeks: TA only OK if good views and measurements adequate, even if >= 5 day
discrepancy between LMP and CRL or unknown LMP Can add TV if this would improve accuracy (technologist discretion)
IUP or POSSIBLE IUP: GENERAL
Endometrial Contents: Gestational sac, yolk sac, fetal pole
Summary of CINEs through uterus REQUIRED on all 1st trimester examination, further detailed below:
(1) Overview of gestational sac/uterus: Single sweep (longitudinal or transverse) through uterus (best TA or
TV) to demonstrate gestational sac morphology and position
(2) Fetal Cardiac activity: short clip demonstrating presence of cardiac motion
GESTATIONAL SAC
-Presence, location, appearance and number of gestational sac(s)
-If there are multiple gestations, document amnionicity and chorionicity
-Sac to be measured (MSD) when:
(1) No FP or FP uncertain
(2) CRL < 12 weeks
NOTE: At 11.1 to 12 weeks, MSD can be omitted if it is difficult to obtain
-Document and measure subchorionic hemorrhage(s), if present;
Comment on location in relation to gestational sac
→ Comment if bleed encompasses < or >= 50% of gestational sac
-Comment on location of developing placenta, if it is seen (should be seen by 10 weeks)
-May say “too early to visualize” if it is not well seen (depending on gestational age)
YOLK SAC
-Document and measure yolk sac
-Report if no yolk sac is seen, if yolk sac is enlarged, or if yolk sac is misshapen or otherwise abnormal
FETAL POLE
-Document and measure embryo/fetus
BRIEF SUMMARY:
LMP/dates <= 13w6d CRL
o If CRL >=84mm add biometry (and provide separate AUA)
LMP/dates >=14w0d biometry
o If Biometry <=13w6d add CRL (and provide separate AUA)
FURTHER DETAILS:
-At LMP/provided dating <= 13 weeks 6 days: measure CRL
Embryo should be magnified and in neutral position
-Use average of 3 discrete measures if all adequate, otherwise choose best
Provide AUA based on CRL
BUT IF CRL >= 84 mm, ADD biometry (BPD + HC + AC + FL)
Biometry: at least 2 measurements of each
-Use average if all adequate, otherwise choose best
Provide 2 separate AUA: Do NOT average CRL and Biometry
(1) AUA for CRL
(2) AUA for Biometry
-At LMP/provided dating >= 14 weeks 0 days = 2nd trimester US: do biometry as per 2nd/3rd trimester US protocol
Biometry: at least 2 measurements of each
-Use average if all adequate, otherwise choose best
Provide AUA based on biometry
BUT IF Biometry <= 13 weeks 6 days, ADD CRL
Provide 2 separate AUA: Do NOT average CRL and Biometry
(1) AUA for CRL
(2) AUA for Biometry
-Cardiac activity, both M-mode and CINE for all:
(1) M-mode image(s): at least 1
→If fetal HR <120, >160 bpm, provide at least 2 M-mode tracings to confirm persistence
On worksheet, document both HR measures and average
(2) CINE video clip of beating heart/flutter
-Anatomy, if visible: Document bladder, stomach, extremities
-CRL >= 11 weeks: Add magnified midline true sagittal image of the fetus in neutral position
DOPPLER on the endometrium (color, spectral, power): most examinations should NOT have
Doppler on the endometrium (or its contents), more specifically:
NO DOPPLER for definite IUP or potential for IUP, including the following:
-No sac and otherwise normal endometrium
-Possible gestational sac (empty or otherwise)
-Well-formed gestational sac (empty or otherwise)
SPECIAL NOTES:
(1) REQUIRED USE OF DOPPLER
Retained products of conception, gestational trophoblastic disease, and other endometrial
mass/abnormality without definite IUP or potential for IUP (as above) – TV imaging:
-CINE greyscale longitudinal and transverse, even if no abnormality identified at time of
examination
-Assess for color if endometrium is abnormal
If color present:
(1) Add spectral
(2) CINE color (best plane)
(2) OPTIONAL USE OF DOPPLER
CRL > = 7mm + NO heartbeat: per technologist discretion to better demonstrate lack of blood flow
(i.e., demise)
NOTE: if CRL < 7 mm + no FHR, do NOT use Doppler
Comments about early pregnancy dating and data to provide: 1. No FP or FP uncertain: MSD measured and associated date documented
**Estimated US gestational age based on MSD – this is just an estimate, CRL will be used for dating when embryo visible
2. + FP & LMP/dates <= 13w6d CRL
o If CRL >=84mm add biometry (and provide separate AUA)
o Provide MSD & associated dates if CRL <12w, but MSD not used for dating
3. + FP & LMP/dates >=14w0d biometry o If Biometry <=13w6d add CRL (and provide separate AUA)
Additional Notes:
-Use “provided dates” or “LMP” or “clinical dates” when possible for expected dating
-Technologists should NOT re-date pregnancy based on other ultrasound(s) unless this dating is being used clinically
-See end of document for ACOG recommendations on pregnancy re-dating based on US – i.e., when OB would use US dates
to formally re-date the pregnancy
Maternal Structures:
**Do not need to include kidneys unless there is specific indication in order**
Uterus (other than gestational sac, yolk sac, fetal pole):
Measurement of size:
-If there is a gestational sac + yolk sac + fetal pole, uterine dimensions and volume do not need to be
performed/recorded.
--> All must be present (if not, please measure, as below)
--> Checkbox on worksheet: "appropriate gravid enlargement" (if this is accurate)
-If 1 or multiple of above are not present (i.e., gestational sac + yolk sac without fetal pole; sac-like structure;
questionable fetal pole; empty endometrium, etc.), uterine dimensions and volume should be performed and
recorded.
--> When measuring:
→ Length in sagittal from fundus to lower uterine segment (include cervix)
→ AP in same sagittal view as length (perpendicular to length)
→ Width in transverse view
→ Provide volume measurement (mL)
→ NOTE, if there is nothing in the endometrium, measure endometrial thickness
Documentation of general appearance:
-Standard sagittal & transverse views
-Document fibroids; measure largest fibroid and any that may be affecting the gestational sac/endometrial
canal
-Do not use Doppler (color, spectral, power) on fibroids
Ovaries and Adnexa:
SUMMARY of when to CINE:
REQUIRED:
(1) No IUP and + b-HCG (i.e., possible ectopic): CINE both adnexa even if no obvious mass is identified, as below
-This includes empty “gestational sac-like structure”
(2) Ovarian/adnexal mass: ectopic or otherwise, detailed below
NOT required: IUP + normal ovaries/adnexa (including typical corpus luteum)
-No need to CINE ovaries with typical corpus luteum cyst
General
-Document and measure each ovary, document corpus luteum (if visible)
-Complete documentation of the ovaries requires several still images through each ovary in two planes per
ACR requirements, even if normal in appearance
Obtain 3 images in longitudinal plane (latmed or medlat) and 3 images in transverse plane
(supinf or infsup)
-Document adnexal regions (even if ovaries are both seen, need at least STILL images of both adnexa)
-If there is no IUP and + b-HCG, CINE both adnexal regions (even if no obvious mass is seen)
-This includes empty gestational sac-like structure
-Document any other ovarian or adnexal mass/cyst
-If mass is identified: provide CINE in multiple planes
-If the mass is near or not definitively separate from the ovary:
→CINE to show mass moving separately from ovary, HOW to:
TV: use probe to separate ovary from mass; if this is not helpful, use non-scanning
hand to push on the abdomen to attempt to separate the ovary from the mass
Comment:
-If mass + ovary move together, it may be ovarian - likely corpus luteum
-If mass and ovary move separately, it is unlikely ovarian - concerning for ectopic
DOPPLER on ovaries/adnexa in pregnancy:
ED patients, all indications:
-Ovaries and adnexa: color only for all patients
-Add spectral to document waveforms ONLY if:
1. Indication is “rule out torsion”
2. Appearance is worrisome for torsion
Outpatient:
-Normal ovaries and adnexa: no Doppler of any kind
-Abnormal ovaries/adnexa or lesion that is not clearly the corpus luteum: color only
-Add spectral to document waveforms ONLY if:
1. Indication is “rule out torsion”
2. Appearance is worrisome for torsion
Cul-de-Sac:
-Evaluate for fluid; if present, document amount and if simple or complex
-ED patient or outpatient for “rule out ectopic” and no IUP: evaluate for fluid in Morrison’s pouch (even if no
pelvic fluid)
-ED patient or outpatient with > = moderate pelvic free fluid and no IUP: evaluate for fluid in Morrison’s pouch
When to notify the radiologist before letting patient go (ED, inpatient or outpatient):
(1) Suspected demise
(2) Evidence of ectopic: either adnexal mass OR complex free fluid
(3) Any other required items on the “Sonographer to Radiologist Communication of Ultrasound Findings”
document.
First Trimester Ultrasound Flow Chart